Okay, dann let's start. Also, welcome for the people watching us remotely or via

the videos for the continuation of our cross linked polymesystem lecture.

Last time we talked a bit about elastomers, which is a big part of the cross linked polymer group.

What characterizes them? We had this nice elastic and elongation, couple of hundred percent,

totally reversible for the polymers. They're very soft. They have immodulus in the scale of mega Pascal to kilo Pascal

compared to the gigapascal of other polymers.

We also talked about what it needs to actually be a rubber. In German we have this difference in determination.

We have kautschuk, which is the uncross linked rubber. And then we have gumi, which is then the cross linked rubber.

So in German we discriminate a bit in English, that's just rubber.

Yeah, so the basic requirements are that we have a very low TG.

So we are very flexible. Our chains are very movable orientable.

If you want to do a cross linked system, it also has to be of course cross linked cable. That's an obvious one.

And what we also do not want to have is crystallinity.

As low crystallinity as possible, because this acts as physical cross linking points.

And we want to do this chemically during our cross linking reaction.

Okay, we also talked a bit about how we classify the elastomers.

This is done by the constitution of the main chain. What we have, what groups or what atoms we got in our main chain will determine to a large extent the properties.

That by it makes sense to do the classification of the elastomers also by that.

Large groups are the R-Rubbers that we will talk a lot about today and next time, which basically have just carbon hydrates in the main chain, but also double bonds.

Later we will talk about the M-Rubbers, which are only saturated carbon hydrates.

The Q-Rubbers, the silicone, and also large group.

And then some special polyester mesh, U-Rubbers and so on.

Last time we started with the most common elastomer, which is still the natural rubber.

We talked a bit about how it was discovered. It's used for three millenials now almost by humankind. And it's still one of the most important and also by just weight or volume.

Most used elastomer, what we still have.

There was a big of a hiccup, actually developing it to a cross linking, to a cross linkable system.

But we talked about that last time already. What is important for you to remember is that this rubber stuff, this is like plant milk.

So these containers with the milk inside, you have to think about latex or the cartridge in his natural form as something like that.

So it's not a biomaterial, but it's a biological product, so it can also go bad.

And the tree is kind of picky. It just wants to sit around the equator where we have 25 to 30 degrees, year round, 2000 millimeters per year, precipitation.

For example, in the Alangin we have 10 degrees sea average temperature and 830 millimeters per year.

So I'm going to be feasible here.

We also have this curiosity that we have a tree originated here in the Central America or close to the Equators of America.

That we have this fungus, Mito-Zyklus Ulai, which will just attack the tree, it decomost the leaves.

So we actually can't do plantation work in the areas where the tree originated.

So this is why these countries where the tree is originating, Havir Basiliensis, Brasile, are actually Cartel net importers.

So most of it is now ground in Central Africa and the growth of it is from Southeast Asia now.

Good. Then we also talked a bit about the polyisoprene, which is the base molecule. We have two different isomines. We have the cysts and we have the trunks.

The cysts is what we want and also nicely what is, to a large extent, in the latex or in the sap we can tap from the Havir Basiliensis tree and also in very, very high purity.

That makes the Havir Basiliensis really nice for collecting, producing the sap.

Other trees, like the Guldapere, are the volatile tree. They also do latex stuff.

Actually many plants do this, this is often the white juice that is secreted by plants, this often contains some latex.

It's just a wound sealant for the tree. So for us, our blood calculates and for the tree it's latex that calculates and covers the wound so it doesn't die or get infected.

The problem with this trunks is that it's crystalline as a high melting point, plus 65 degrees C, which is over most used temperature.

We have in our common environments. The TGs are quite similar, minus 70 degrees C. Anybody asks you what's the TG of natural rubber, say minus 70 degrees C?

For this we have almost no crystallinity and if we get some small ones we have a melting point of 23 degrees C.

This is very low, we can easily get rid of that just by storing it.

That was just a quick recap because we had quite some interruption. So you're again a bit familiar with our natural rubber basics.

As I already told you, the natural rubber is...

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